Pyrolysis oil or bio oil has been studied as a possible low CO2 foot print sustainable substitute for fossil fuels. It is formed by a process called “fast pyrolysis” where dry biomass is heated rapidly to temperature of 450-650° C. in the absence of oxygen, held for a short time (a few seconds or less), and rapidly cooled to produce a condensate. The condensate from this process contains a very high level of oxygenated components, phenolic/aromatic compounds and water in a viscous emulsion. Since the condensate is from a non-equilibrium process, the components are not stable with one another and the oil emulsion continues to degrade with time. This makes it distinctly different from petroleum based oils and has hampered the commercial implementation to date.
The “water” and other highly oxygenated molecules in pyrolysis oil are fully emulsified and do not phase separate readily like water does in the presence of standard fossil fuels. The density of pyrolysis oil is much higher than diesel. The oxygen content is about 40-50%, and no sulfur is detected normally. The cetane number is only about 10, whereas diesel engines typically operate in the 40-55 cetane number range. The viscosity increases to a maximum in period of 12 months due to continued polymerization. The pyrolysis oil is not stable with air and continues to de-gas upon storage. Pyrolysis oil cannot be readily blended with diesel.
Thus, stabilization of the bio-oil is essential to its utilization. Like crude oil, bio oil (pyrolysis oil) can be fractionalized and refined to yield products with specific properties and characteristics as required for various downstream options. U.S. Pat. Nos. 4,209,647, 4,508,886, 4,233,465 and 4,942,269 disclose methods for separating lignin and phenolic fractions from bio oil obtained by pyrolysis of lignocellulosic materials and the subsequent use of that fraction in making of phenol-formaldehyde resins. However, these processes involve a series of liquid and liquid extraction steps. The complexity and lengthy solvent extraction associated with a relatively low yield of the phenolic components limit the industrial applications of such a process.